Conventionally, there has been proposed a spread spectrum communication device which demodulates a received analog spread spectrum signal by the direct spectrum spreading scheme by performing both the analog signal processing operations and the digital signal processing operations.
Regarding such a spread spectrum communication device, for example, the Japanese Publication for Laid-Open Patent Application No. 115387/1995 (Tokukaihei 7-115387) discloses the following technique. An A/D converter for receiving an analog spread spectrum signal and converting the received analog signal to a digital signal is provided at the first stage of a base band processing unit so that digital signal processing operations are performed at the stages there behind in the base band processing unit.
Further, regarding a spread spectrum communication device, the Japanese Publication for Laid-Open Patent Application No. 83486/1997 (Tokukaihei 9-83486) discloses the following technique. An integrating unit for conducting an integrating operation with respect to an analog input signal with weights given thereto according to a PN code and outputting an integrated result as an analog output signal is provided. By doing so, the analog output signal is intermittently held, and peaks of the analog signal thus held are detected so that timings of the detected peaks are determined, and only at these timings thus determined, peak values of the inputted analog signal are digitized by an A/D converter.
With the technique disclosed by Tokukaihei 9-83486, an operational speed of the A/D converter can be suppressed to minimum, thereby resulting in that power consumption can be reduced.
However, with the technique disclosed by Tokukaihei 7-115387, since a sampling operation has to be carried out many times at a high speed for synchronization acquisition, there has arisen a drawback in that a circuit size thereof is large and power consumption thereof is great.
Besides, with the technique disclosed by Tokukaihei 9-83486, power consumption of the base band processing unit can be suppressed by lowering the operational speed of the A/D converter, but this makes the circuit for detecting peaks of an analog signal complicated. Thus, values obtained by peak detection with respect to the analog output signal are subject to A/D conversion, and therefore, there is a drawback in that precision in peak value detection is poor in spite of complicated peak detection. Therefore, there has arisen a problem that an analog spread spectrum signal is hardly demodulated with high precision.